Liquid crystal display device is a passive light emitting device, which does not emit light by itself, and requires a backlight module to provide light for the liquid crystal panel, so as to display images. Since the backlight module used in a liquid crystal panel has thin, light and power saving characteristics, it is employed in the display devices widely.
Currently, the backlight techniques used in liquid crystal display device mainly comprise: Cold Cathode Fluorescent Lamp (CCFL) and Light Emitting Diodes (LED).
Since the LED backlight module has advantages such as high brightness, high color purity, long life, good reliability, without mercury pollution, etc., the proportion of the LED backlight module is gradually increased in backlight modules.
LED backlight modules can be classified as direct type and side type based on the optical structure. The side type backlight module arranges the light source on a side of the panel; while the direct type backlight module arranges the light source below the panel. As shown in FIG. 1 and FIG. 2, FIG. 1 shows a structural schematic diagram of a direct type backlight source in the prior art; FIG. 2 shows an arrangement of LED lamps in the direct type backlight source in the prior art. The direct type backlight module mainly comprises: a back board 01, a circuit board 02 located in the back board 01, LED lamps 03 distributed with intervals, a reflective sheet 04, a diffusion plate 05, an optical membrane 06, a side reflective sheet 07 and a prism sheet 08, etc.
The light emitted from an LED lamp can be regarded as a point light source; since the light emitted from an LED lamp has a certain light emitting angle, the light intensity of the backlight module may be relatively high in a certain direction, while be relatively low in an other certain direction.
In the prior art, to obtain a homogeneous illumination, the number of the LED lamps or the light mixing distance (which is generally indicated by the distance H from the top of the bottom reflective sheet 04 to the bottom of the diffusion plate 05 in FIG. 1) of the backlight module should be increased, this results in the increase of the cost or the thickness of the backlight module. Moreover, for a certain number of the LED lamps in the backlight system, if the thickness of the backlight module is reduced, the incident light on the display panel may be inhomogeneous, such that obvious spots can be observed on the display device.